Evacuating audion tube



Patented Jan. 22, 1929.

PATENT OFFICE.

UNITED STATES.

ERNEST ANTON LEDEREB, OF BLOOMEIELD, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

EVACUA'IING AUDION TUBE.

This invention relates to evacuating vessels and more particularly to a method of and apparatus for completely exhausting and cleaning-up all residual gases from electron tubes but is readily applicable to any vessel in which a vacuum is desired.

In electric lamps and electron discharge devices of the evacuated type, it is necessary that a high degree of vacuum be attained for it is well known that the higher the vacuum the more eflicient the resulting product and the longer its life. Vacuum pumps of very efiicient type have been designed to exhaust vessels to a degree corresponding to a pressure of about 10- mm. of mercury but it has not been found economical to utilize such pumps in production practice. Under factory conditions the greatest degree of vacuum to be obtained with economy corresponds to a pressure of about 1 micron or 10 3 mm. of mercury and for that reason resort must be had to other expedients, such as clean-up agents, to complete the evacuation.

These clean-up agents serve to absorb or combine with gases and moisture, if any, residual on the interior portions of the vessel and with the gases occluded within the metal structure enclosed by the vessel, in such a manner as to. prevent those gases from ever having a deleterious effect on the vital elements of the structure. However, many serious difficulties attendant upon the usedof clean-up agents have been encountere It is therefore an object of my invention to reduce, if not entirely eliminate, the disadvantages accruing under present methods of exhausting and cleaning-up gases in vessels of the type described.

Another object of this invention is to provide a method of exhausting vacuum devices containing a vaporizable clean-up agent which will permit the enclosed parts to be heated to a high temperature without vaporizin said clean-up material.

It is a rther object to provide apparatus suitable for the purpose and still further objects will become apparent from the description, from the claims and from the drawing in which:

Fig. '1 is a diagrammatic view of an electron discharge tube illustrating one phase of my invention.

Fig. 2 is an inverted view of the device :hgwn in Fig. 1 after sealing off the exhaust Figs. 3 and 4 are views corres onding to Figs. 1 and 2 respectively, but 0 a modification, and

Fig. a is a diagrammatic representation of a machine that may be used in working m invention.

In manufacturing vacuum tubes by the present practice, the mount, which is the flare tube or stem carrying the electrodes and lead-in wires, after completion, has a small piece of magnesium, aluminum or other metal of similar character aflixed to it by clamping or the like, so that it may be sealed within the bulb. The mount is then sealed to the bulb and the bulb is connected tothe exhaust pump through its tubulature. During the exhausting period the bulb-is baked at from 420 to 500 cent-igrade to drive out moisture and gases adhering to the walls of the bulb and to the mount and to drive out any gases or moisture occluded w thin the metal of the metal portions.

After the vacuum tubes have been baked and exhausted fora predetermined time, that is, for such time as may be found necessary to reduce the ressure within them to about 10-- mm. o mercury, they are tipped-off and based preparatory to flashing or volatilizing the magnesium or aluminum clean-up agent with appropriate seasoning to further reduce the pressure to about 10- 5 mm. The flashing may then be, accomplished by any appropriate method of induction heating such as that described 'in the patent to Northrup #1386394, patented Dec, 3, 1919. This serves to completely remove or render inactive all deleterious gases remaining after exhauston by the pump.

It has been found, however, that the above method has certain serious disadvantages for quantity or factory production. It is difficult to secure the metal clean-up agent to the plate electrode, to which it is most usually aflixed, in a proper manner with e ediency and so that the plate may be hig 1y heated to a dull red heat to drive out "occluded gases, even by highly skilled operators. The exhaust baking must be done at temperatures below the softenin point of a large amount of deleterious gas may remain to be evolved during the lifeof the device. Such are few of the most important difliculties encountered.

By my invention I obviate these troubles and provide an eflicient and economic process readily adaptable to factory production. Briefly I so prepare the mount that a cleanup agent maybe movably positioned thereon so that it may be positioned well out of the zone of heating during the sealing-in and baking-out operations and may thereafter be removed to a position'where it will be available for volatilization or flashing. I prefer to utilize the principle of inductive heating for both baking-out and flashing operations and as the former is amply described in the patent to J. B. Pratt #1,374,67 9, issued April 12, 1921 and the latter in the appli cationof Harvey C. Rentschler, Serial No. 582,261, filed August 16, 1922, vacuum devices and method of exhausting the same, and assigned to the Westinghouse Lamp Company, they will not be more particularly described.

Referring to Figs. 1 and 2 of the drawing,

a mount of stem, generally designated 2, and

comprising a flare 4, leads 6, press 8 and electrodes, generally designated 10 (the plate elect-rode alone being shown), is sealed into the bulb 12 at 14. To the bulb 12 is attached an exhaust tube 16 having a constricted portion 18 communicating with the interior of the bulb. Fixed to the usual plate 10, of nickel, molybdenum or the like, or forming part of the mount supporting structure, is a wire or the likeprojection 20 adapted to receive a loop or other form of clean-up agent 22 slidably thereon, the end 24 of theprojection 20 being so bent or deformed as to prevent the agent 22 from sliding off. An induction coil 26 is shown surrounding the device in both figures.

Immediately subsequent to the sealing-in operation and before the heat given to the bulb by the sealing-in operation has been dissipated, the bulb may be placed in an in verted position (see Fig. 1) on an exhaust machine and exhausted while being baked out. If the bulb has not been allowed to cool for too great a time between its removal from the sealing-in machine and its insertion in the exhaust machine, gases and moisture that have been driven from the interior surfaces of the bulb will not re-condense or redeposit thereon and induction heating of the metallic structures within the bulb will suffice to completely drive out all occluded gases. During this induction heating or baking-out, the magnesium or other metal clean-up is positioned out of the most direct 'nfiuence of the coil 26 and, as the wire 20 is f iron or other metal of low heat conductivity, will not be volatilized by the heating effect of the high frequency induction.

Since the glass parts of the device are not heated by the high frequencyinduction I am able to bake-out the metallic structures at a temperature much higher than that heretofore attainable without volatilization of the clean-up agent and in fact to temperatures approximating the melting point of nickel, 1460 (3., (if the plate be of that metal), or, in other words, temperatures approximating the melting or volatilizing point of that metal of the structure having the lowest melting point. Then too, since the baking-out is accomplished before any volatilized metal has coated the interior surfaces of the vitreous container or bulb, the glass is not heated excessively and suck-ins are entirely avoided.

The tubes after evacuating are tipped-oil, based, and placed by their bases, in adevice (not shown, but which may be similar to the machine of Fig. 5 to be described) constructed and arranged to subject them to induction heating to volatilize the clean-up agent. When the tube is inverted or swung through 180 to this position, the clean-up agent 22 will fall tothe position designated 28, as shown in Fig. 2, now within an induction coil 26. Thereupon the tube is arranged in a suitable receptacle or holder (not shown) which may be adapted to be posi-- tioned on the machine of Fig. 5, for induction heating of the cleanup agent to volatilize it.

In Figs. 3 and 4 I have shown a modifica tion of the arrangement of Figs. 1 and 2, wherein the clean-up agent 22 is coiled around or otherwise movably arranged upon the support and lead 32 of the plate electrode 34, whereby the tube is adapted for exhaustion in the position of Fig. 3 and for flashing in the position of Fig. 4:

In pursuing these methods, I am enabled to combine the baking-out and exhaust operations in manners more satisfactory than any of which I am aware and I am also enabled to obtain an exceedingly high vacuum in the tube with the advantages obviously accruing.

Fig. 5 is a diagrammatic representation of a machine adapted for baking-out and exhausting and comprises a table'or turret 36 suitably driventhrough hollow spindle 38 by drivin means not shown, gearing 40 to drive shaft 42 and cam roller 44 (all in the direction of the arrows), a cam follower 46 so connected to the insulating block 48 carrying induction coil 26 by means of push-rod 50, that for a predetermined rotation of the table 36 the coil 26 will be lowered over tube 2 to the approximate positionshown in Fig. 1, and for the next equal movement will be removed therefrom. It will be understood that suitable indexin mechanism will be arranged in conjunction with the machine for this purpose. I may also provide induction coils of the same or varying power at several or all indexing positions of the CPI machine, so that all gases may be effectively driven out while the tube is on the pumps. This makes it possible to utilize gases evolved from the highly heated metal structure to remove or sweep out all traces of harmful residual gases. It will thus be understood that by my method, I am enabled to completely remove or render inactive, all gases whether residual within the tube or op cluded Within the glass or structure there- 0 Various modifications of my invention may be readily perceived and for that reason I desire to be limited only by the scope of the appended claims.

What is claimed is:

1. The method of manufacturing electrical devices, having an evacuated container, comprising positioning a clean-up agent movably in said container, heating portions of said device to drive out gases therein while maintaining the said agent in a substantially unheated portion thereof and thereafter moving said agent to a heat-affected position to render the same active for cleaning up residual gases.

2. The method of manufacturing electrical devices, having an evacuated container provided with a metallic electrode, com rising positioning a clean-up agent mova l in said container, heating said electrode to rive out gases therein While maintaining said agent spaced from said electrode, re-positioninrr said agent adjacent said electrode and re eating the electrode to volatilize the clean-up agent.

3, The method of exhausting a vacuum device comprising disposing a volatile clean-up material therein in a position spaced from the electrodes of said device, heating the electrodes during exhaustion to a temperature above the melting point of the clean-up material, sealing off said device, positioning said clean-up material in contact with one of said electrodes and heating the electrode to vaporize the clean-up material.

4. An intermediate product in the manu facture of electrical devices of the character described, comprising a sealed envelope, a mount therein having an electrode and a clean-up agent disposed adjacent said electrode and movable into contact therewith.

5. An intermediate product in the manufacture of electrical devices of the character described, comprising an envelope, an electrode therein, a support for said electrode and a relatively volatile metal displaceably coiled about a portion of said support.

.In testimony whereof, I have hereunto subscribed my name this 25th day of March, 1924.

ERNEST ANTON LEDERER. 

